1. Field of the Invention
The present invention relates to novel metallocene compounds useful as components in polymerization catalysts, to catalysts comprising such metallocene compounds, to a process for the polymerization of olefins and to particularly propylene, and olefin homopolymers, random, and impact copolymers prepared by using the metallocene catalysts.
2. Background of the Art
One of the most important factors determining the success of a catalyst is its versatility, that is the possibility to use it for the broadest possible range of products. For a long time, the limitations for the development of metallocene catalysts for polypropylene has been their inability to produce propylene-ethylene copolymers of high molar mass, due to the fact that ethylene behaves as a chain transfer agent with most metallocenes. This effect has been observed for all basic metallocene structures, such as the syndiospecific Cs symmetric Me2C(Cp)(Flu)ZrCl2, the aspecific C2v symmetric Me2Si(Flu)2ZrCl2, and both the C2 symmetric rac-Me2C(3-iPr—Ind)2ZrCl2 and the fluxional (2-Ph-Ind)2ZrCl2 catalysts for elastomeric polypropylene. This effect has also been found for the isospecific C2 symmetric rac-Me2Si(2-Me-4,5-Benz-Ind)2ZrCl2 and rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 [L. Resconi, C. Fritze, “Metallocene Catalysts for Propylene Polymerization” In Polypropylene Handbook (N. Pasquini, Ed.), ch. 2.2, Hanser Publishers, Munic 2005]. While the 2-Me substitution of this catalyst family suppresses the β-hydrogen transfer to the propylene monomer and thus prevents the formation of low molar mass polymer, it fails to prevent the β-hydrogen transfer to the ethylene comonomer in case of the latter's presence. This β-hydrogen transfer to the ethylene comonomer becomes the favored chain termination mechanism and leads to the formation of low molar mass propylene-ethylene copolymers [A. Tynys et al., Macromol. Chem. Phys. 2005, vol. 206, pp. 1043-1056: “Ethylene-Propylene Copolymerizations: Effect of Metallocene Structure on Termination Reactions and Polymer Microstructure”]. Exceptions have been found in some zirconocenes with highly bulky ligands, such as rac-Me2C(3-tBu-Ind)2ZrCl2, which show a marked increase in molar masses by ethylene incorporation. This catalyst, however, has shortcomings in terms of homopolymer molar mass and activity.
Another key requirement of a metallocene catalyst is its capability to produce polypropylene with a high melting point. This is equivalent with a catalyst that has a very high stereospecificity and regioselectivity. Within the rao-Alk2Si(2-Alk-Ind)2ZrCl2 catalyst family, the stereospecificity and regioselectivity has continuously been improved during the last 15 years. EP-A1 834 519 relates to metallocenes of the rac-Me2Si(2-Me-4-Ar—Ind)2ZrCl2 for the production of high rigid, high Tm polypropylenes with very high stereoregularity and very low amounts of regio errors. Although not tested for their copolymerization performance, the metallocenes disclosed in EP-A1 834 519 anticipated substitution patterns in 2-position that would later be identified as particularly suitable for the production of propylene/ethylene random copolymers when combined with additional substituents in certain positions. However, the highly stereo- and regio regular polypropylenes were not obtained under commercially relevant process conditions and suffered from too low activity/productivity levels.
US-A1 2001/0053833 discloses metallocenes having substituents in 2-position consisting of an unsubstituted heteroaromatic ring or a heteroaromatic ring having at least one substituent bonded to the ring. Such catalysts afford C3/C2 copolymers with reasonably high molar mass, but fail to produce high Tm homopolymers under conditions typical for commercial scale production, i.e. on a support and at temperatures from 60 deg C. and higher. Also, the productivities of this catalyst family are unsatisfactory.
WO 01/058970 relates to impact copolymers having a high melting point and a high rubber molar mass, produced by catalysts comprising metallocenes of the rao-Me2Si(2-Alk-4-Ar—Ind)2ZrCl2 family. High molar masses in the propylene/ethylene rubber were achieved when both Alk substituents were i-propyl groups. WO 02/002576 discloses bridged metallocenes of the (2-R-4-Ph-Ind)2ZrCl2 family having particular combinations of substituents in the 2-positions of the indenyl ligands and substituents in the benzene ring. A high polypropylene (PP) melting point is favored if the Ph group exhibits a substitution pattern in the 3 and 5 positions, particularly in case of butyl substituents. A combination of high homopolymer melting point and high copolymer molar mass is achieved if both substituents R in 2-position are isopropyl groups. The major shortcoming is the very low activity/productivity of the rac-Me2Si(2-R-4-Ar—Ind)2ZrCl2 catalysts if both ligands R are branched in the α-position. WO 03/002583 discloses bridged metallocenes of the (2-R-4-Ph-Ind)2ZrCl2 family having particular combinations of substituents in the 2-positions of the indenyl ligands and the 4-Ph substituents. A high PP melting point is favored if the Ph group exhibits a substitution pattern in the 2-position, particularly in case of biphenyl substituents. A combination of high homopolymer melting point and high copolymer molar mass is achieved if both substituents R in 2-position of the indenyl ligand are isopropyl groups. One major shortcoming is the very low activity/productivity of the rac-Me2Si(2-R-4-Ar—Ind)2ZrCl2 catalysts if both ligands R are branched in the α-position. Moreover, the highest possible molar masses of the homopolymers produced by using such catalysts are relatively low which corresponds to relatively high melt flow rates. This, in turn excludes such metallocenes from catering applications such as pipe, blown film, cast film and injection stretch blow molding.
EP-A2 1 250 365, WO 97/40075 and WO 03/045551 relate to metallocenes having substituents in the 2-positions of either of the indenyl ligands with the imperative that at least one of the ligands in 2-position is branched or cyclicized in the α-position. WO 04/106351 relates to metallocenes having substituents in the 2-positions of the indenyl ligands with the proviso that one ligand is unbranched or bound via an sp2-hybridized carbon atom and the other ligand is branched in the α-position. Such catalysts afford high Tm homopolymers and high molar mass propylene/ethylene copolymers. However, there still are limitations with regard to catalyst activity/productivity and lowest achievable homopolymer melt flow rate.
PCT/US2007/022614, a co-pending applications by the present inventors, demonstrated that metallocenes having ligands being β-branched in the 2-position created surprising increases in activity of the metallocene catalyst and also created products with unexpectedly superior properties than previously known metallocenes. The inventors now have discovered a species of the previously revealed genus that unexpectedly produces even significantly higher increases in catalyst activity and improvements in product properties.
In summary, the main deficiency of supported catalyst systems comprising metallocenes of the above mentioned prior art, is that so far no catalyst has been found that, when used for the homopolymerization of propylene, affords isotactic polypropylene with a high melting point and very high molar mass (or very low melt flow rate) and that, when used for the copolymerization of propylene with ethylene, affords high molar mass propylene/ethylene copolymers, all at very high catalyst productivity. As a consequence, when compared to Ziegler/Natta catalysts, the industrial usefulness of these catalysts is limited because certain applications that require a combination of a high melting point, a very low melt flow rate, and/or a high molar mass copolymer or copolymer component, such as in impact copolymers, are not available at cost competitive productivities.
An object of the present invention is to address this shortcoming of the state of the art metallocene compounds and to provide metallocenes that increase desirable characteristics such as high melting point, high molar mass homopolymers and high molar mass copolymers, and do so at higher productivities when used as components of supported catalysts under industrially relevant polymerization conditions at temperatures of from 50° C. to 100° C. In addition, the inventions of the current example provide these advantages by using a metallocene with symmetrically substituted 2 positions on the indenyl group. This is significantly more cost effective, and therefore far more desirable, than the comparative examples that have asymmetric substitution.
Another objective of the present invention is to provide a process for the polymerization of olefins, particularly propylene, ethylene, and optionally one or more higher 1-olefins.
Furthermore, it is an objective of the present invention to provide olefin polymers, particularly propylene homopolymers, random copolymers of propylene with ethylene and/or higher 1-olefins, impact copolymers comprised of propylene, ethylene and/or optionally higher 1-olefins, and random impact copolymers comprised of propylene, ethylene and/or optionally higher 1-olefins.